It is narrated from Sayyiduna Abu al-Darda' (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) saw a pregnant woman at the door of a fustat or a khiba' (tent), and he (peace and blessings be upon him) said: "Perhaps her owner has intercourse with her? I intended to curse him with a curse that would enter his grave with him. How can he make him his heir when that is not lawful for him? And how can he take him as a slave when that is not lawful for him?" Imam Muslim (may Allah have mercy on him) narrated it in his Sahih from Muhammad bin Bashshar, from Abu Dawud. Al-mujihh means being pregnant, or carrying a burden. This is because he sees that she is pregnant while she is not pregnant (that is, not yet pregnant from his seed); then he comes to her (that is, has intercourse with her) and she becomes pregnant from him, and he considers the child a slave while he is not a slave. What is meant by it is that he (peace and blessings be upon him) forbade having intercourse with captive women before istibra' (establishing that the womb is free). Imam Muslim (may Allah have mercy on him) narrated it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15590